Known automatic or automated motor vehicle transmissions as a rule have a parking lock by way of which a transmission output shaft can be mechanically fixed. Besides a purely mechanical system for actuating of such a parking lock with an active mechanical connection between a selector lever operated by the driver inside the motor vehicle and the parking lock in the transmission, electro-mechanical and electro-hydraulic systems for actuating such a parking lock are also known from DE 41 27 991 C2. The parking lock in the transmission is connected by an active electric connection to a selector device operated by the driver inside the motor vehicle and the parking lock can be actuated electro-mechanically or electro-hydraulically byway of a parking lock function implemented in an electronic control unit of the transmission and as a function of other operating parameters of the motor vehicle.
Furthermore, various methods for automatically engaging such a parking lock are known. For example, in U.S. Pat. No. 3,937,105 it is proposed to engage the parking lock of the transmission automatically and independently of the drive position selected by the driver if an ignition circuit of the motor vehicle is interrupted and simultaneously the motor vehicle is still rolling at a speed lower than a defined, low threshold value.
From U.S. Pat. No. 4,892,014 a method is known, in which the parking lock of the transmission is automatically engaged by an electric motor if an ignition circuit of the motor vehicle is interrupted and simultaneously the speed of the vehicle is below a defined low threshold value, but also if the driver's door of the motor vehicle is open and simultaneously the driver's seat in the motor vehicle is unoccupied and simultaneously the speed of the vehicle is below the low threshold value. In both cases, it is provided that when the parking lock is engaged automatically, in addition a parking brake of the motor vehicle is automatically actuated. In U.S. Pat. No. 4,892,014 it is also proposed that when the ignition circuit is engaged, but without the drive engine of the motor vehicle running, the transmission is automatically shifted to its neutral position by an electric motor without this having to be done by the driver.
Finally, from EP 0 814 287 B1 a method for automatically engaging the parking lock of an automatic transmission is known in which the parking lock in the automatic transmission is automatically engaged by the transmission control unit when the speed of the vehicle is zero and simultaneously an ignition circuit has been interrupted and, as a further condition, either a predetermined time interval after the interruption of the ignition circuit has passed or a door of the vehicle is open, but at the latest when—and in that case as the sole condition—the ignition key has been removed from the ignition lock. To achieve better availability of the vehicle, as a special feature in all three cases the engagement of the parking lock is prevented, directly before switching off the engine or within a predetermined time interval after the engine has been switched off, if the driver has selected neutral by way of the selector lever.
The purpose of the present invention is to provide a method alternative to those of the prior art for the automatic engagement of a neutral position and a parking lock in an automatic or automated transmission of a motor vehicle, which secures the motor vehicle sufficiently well against starting or free rolling unintended by the driver, and avoids changes of the operating condition of the transmission or the vehicle that could take the driver by surprise while interfering as little as possible with the vehicle's ability to be driven or operated.